The present invention relates to a display device, and especially relates to a display device preferable for using for improved safety and reliability in a case of monitor-display in industrial plant equipment.
Conventionally, in large-sized industrial plant equipment, an observer has monitored an operation condition of the plant on a display device in a monitoring room to deal with, for example, variation and accidents. In particular, for example, in an atomic power plant, high safety is required, thus monitoring the plant has important responsibility.
A technique that enhances safety in a screen display system of an electric power company is disclosed in Japanese Patent Application Laid-Open No. 2010-3092. The screen display system in Japanese Patent Application Laid-Open No. 2010-3092 is “a screen display system that displays a management screen on a display unit of an operations management calculator, including priority order data that specifies a priority order of execution tasks for a plurality of tasks including a task that generates the management screen to display, and including execution task determining means that determine an execution task based on the priority order data, and change image display means that change an image displayed on a part of the display unit to a different image, wherein a task that the change image display means changes an image displayed on a part of the display unit to a different image is lower than a task that generates the management screen to display, in the priority order in the priority order data” (Claim 1). Furthermore, a technique that attempts to enhance reliability of a display device by redundancy is disclosed in Japanese Patent Application Laid-Open No. 2000-172482. A high reliable display device in Japanese Patent Application Laid-Open No. 2000-172482 is “a high reliable display device by multiplex computer systems including at least two computer systems that control an image signal, switch means that switch each of the computer systems, and display means that display an image based on the image signal transmitted from the computer system switched by the switch means, wherein each of the computer systems includes display storing means that store the image signal transmitted to the display means, and the switch means read the image signal stored by the display storing means to cause the display means to display the image, and when the computer system that transmits the image signal is broken, until a taking-over process of the image signal to another switchable computer system is completed and the switch means switch the other computer system to the display means, update of memory content by the display storing means that belongs to the broken computer system is forcibly stopped, and the switch means causes the display means to display a screen based on the image signal before the breakdown of the broken computer system” (Claim 1).
In the above-described technique disclosed in Japanese Patent Application Laid-Open No. 2010-3092, an observer visually determines large change of display, such as disturbance of screen and disappearance of display, when there is a trouble on a display device that a control/monitor system of conventional large-sized plant control system or large-sized electric generating facility employs. However, there is a problem that when diagram shapes, colors, and characters of a part of a state display such as video information are changed to incorrect diagrams and characters by breakdown that has occurred in software and a drawing circuit that display drawing data on a display panel such as a liquid crystal display in the display device, it is difficult for the observer to quickly recognize its correctness/incorrectness. There has been a problem that in the system that displays a control/monitor system state on, for example, the display device that the above-described large-sized system employs to monitor and control, the display on the screen hardly changes in many cases unless special events such as an ON/OFF operation, an abnormal detection, and an abnormal stop of the system occur, thus it is difficult for the observer to quickly determine even when the display device is broken to freeze.
For example, nuclear power plants have a considerably severe safety level (electron system is equivalent to SIL3 to SIL4 of IEC61508 standard) in many cases, and especially for a device that displays control/monitor state of a protective system, such as forcible water injection and vent in case of an abnormal occurrence in a monitoring display device of a nuclear reactor and a control system, compliance to the severest safety criteria may be required.
The above-described technique disclosed in Japanese Patent Application Laid-Open No. 2010-3092 employs, as a method that detects a freeze state of display system, a method that disposes a process task that changes the image on a process of a control processor, and then lowers an execution priority order of this process task than that of a display process task of an ordinary operation to detect the freeze state without trouble in an ordinary display. In this display method in Japanese Patent Application Laid-Open No. 2010-3092, it is not possible to detect display failure such that only a part of display is superficially misread as a normal display by malfunction of the process task. It is also difficult for the observer to detect a mistake only by looking the display device.
The above-described display device in Japanese Patent Application Laid-Open No. 2000-172482 duplicates the display system to cause one of the display systems to wait, and then switches in case of trouble of the display system to improve availability. In this display device in Japanese Patent Application Laid-Open No. 2000-172482, especially for monitor display of the plant, it is not possible to detect a mistake in drawing data, and it is also not possible to detect malfunction of the process task.
The present invention is made to address the above-described problems. The purpose of the present invention is to provide a display device that improves safety and reliability, when severe safety criteria are required such as in a case of monitor-display in industrial plant equipment.